It may be recognized that an engine operating on a single type of fuel may be tuned to optimize the trade-off in performance, for instance, horsepower, fuel economy, and/or emissions for the target fuel. However, for engines that operate on fuels that may vary in composition, or for engines that operate on fuels that are blended from separate components, the performance of the engine may typically be limited by that obtainable for only a single fuel or blend. For example, an engine optimized for gasoline-fueled operation may be calibrated by the manufacturer to deliver an optimized combination of fuel economy, performance and emissions. That engine may not exhibit an optimized combination of fuel economy, performance and emissions when operated on a blend of, for instance, ethanol and gasoline. This may be due to the fact that gasoline and an ethanol-gasoline blend are relatively different in such properties as volatility, fuel heating value, octane number and flame speed.